This invention relates to steels, and, more particularly, to a microalloyed steel useful in railway joint bars.
Railway joint bar is a special steel section that is used to join two railroad rails together. The rails are placed end to-end on the ties, and anchored in place with spikes driven into the ties. This procedure holds the rails generally in place, but the ends of the rails would not remain properly aligned with each other without the use of the joint bar. Lengths of joint bar are fastened to the sides of lengthwise adjoining rails in an overlapping fashion so that the joint bar extends from one rail to the other, with bolts that pass through the joint bar and the rails. One length of joint bar is on the inside of the rails and a second length is on the outside of the rails. The joint bars hold the facing ends of the two rails in the end-to-end aligned position.
The joint bar final product must meet specifications established by the American Railway Engineering Association, known in the industry as AREA. The AREA specification requires a minimum yield strength of 70,000 pounds per square inch (psi), a mimimum tensile strength of 100,000 psi, a minimum total elongation of 12 percent, and a minimum reduction in area of 25 percent, and further requires that the steel pass a 90 degree longitudinal bend test.
For over 70 years, the joint bars have been made in one of two ways. In the first, a plain carbon steel having at least 0.45 percent (all compositional percents herein are by weight) carbon is hot rolled to the joint bar section and air cooled. In the second, a plain carbon steel having from 0.35 to 0.60 (preferably 0.45) percent carbon is hot rolled to the joint bar section, air cooled, and then reheated and oil quenched in a separate operation, to give it a higher strength than can be attained without the post-rolling heat treatment. The second approach is more widely used today, because it results in higher strength and better toughness of the final product.
The oil quenched carbon steel joint bar meets the specifications, but it is comparatively expensive to produce. The reheating and oil quenching heat treatment is an additional costly production step, and it would be preferable to have an acceptable joint bar that does not require such heat treatment during manufacturing. Additionally, even though the area specification does not include a toughness standard, the railroads have become more concerned with the toughness of rails and joint bars in recent years. The joint bars produced by the existing approach have acceptable toughness, but improvements in this important property are always welcome.
There, therefore, exists a need for an improved joint bar and a steel for its manufacture. Such a product would desirably not require expensive heat treating operations such as reheating and oil quenching, and would have properties improved over those available with existing processing. The present invention fulfills this need, and further provides related advantages.